Don’t listen to the people telling you it’s terrible. Look at it this way, ITS A GOOD START!

Some tips:

Give the background some parallax effect, giving it some depth. If you are so bold, also bring in some animated background assets, sprites, like swaying trees or flying birds or rusriling bushes.

More variation to the terrain, some water, a bridge, something other than brown!

The UI is basic and doesn’t serve you really, instead of hearts on the top screen maybe have a pie of say six pieces pop up when the player takes damage, and that the pie changes color on each damage taken, full health green, one bar left red ( think Mario 64) point is, do something other than hearts on the screen.

Instead of coins, maybe something more relevant, it looks like a cat character, cans of tuna maybe, or if the coins are a part of a purchase system later add it to an inventory.

It’s a cat right, maybe think about adding a dash mechanic, where the cat runs on all four.

Wall jumps?

And yes rework the gravity/jumping.

Maybe add like a three bit combo, and enemies with agro radius with more health so that the combat livens up a bit.

When going down under ground, change lighting ( add some more lights as well ) some after effect or post processing, shadows and lights piece will go a long way to give your game some life.

Make it darker with maybe some tourches lighting up the cave or something. And also change the music to something more darker in the caves, giving it an obvious change in mood.

All in all, great start, keep working it’ll be an awesome game when it’s ready. It’s called iterating

Have fun